1. Field of the Invention
The invention relates to railroad communication systems for controlling one or more units or groups of remote units from a lead unit.
The invention also relates to air brake systems for use in a train having one or more remote units or groups of remote units controlled from a lead unit in which information concerning the air flow into the brake system at the remote units is monitored and analyzed, the result of which is telemetered to the lead unit.
The invention also relates to air brake systems for trains which are not succeptible to pressure changes in the brake pipe system caused by temperature variations or leakage.
2. Description of the Prior Art
U.S. Pat. No. 3,380,399 discloses a train control system in which a lead unit controls the operation of one or more remote units through communications transmitted between the lead unit and the one or more remote units over a half duplex channel using frequency shift keying (FSK) to serially transmit control information regarding a plurality of functions of the train. In that system, a total of 38 bits of information are transmitted in each half duplex communication. The lead unit and each remote unit store a four bit address code which can be used to define sixteen addresses. The four bit address code is used to determine if radio transmissions should be processed by any receiving unit by matching the address code contained in the received message with that stored at the receiving unit. The use of a single common address does not assure against the remote possibility that other units, in another train in proximity to a receiving unit, are activated by the control information being transmitted to the receiving unit or that information transmitted by a remote unit is processed by the lead unit of another train. The system controls the time that transmissions are made from various units within the same train in accordance with a fixed delay.
Locomotive control systems are presently marketed which utilize the basic concepts described in U.S. Pat. No. 3,380,399. These systems are improvements of the systems of U.S. Pat. No. 3,380,399. Such systems contain a system for preventing the simultaneous transmission of messages by any one of a plurality of units within one or plural trains within transmitting range of each other. Simultaneous transmissions can at time under specific circumstances lock up the communications channel between various trains within transmitting distance of each other thereby preventing effective command execution which can at times include plural trains in proximity to a train yard. Present systems normally use a 62 ms delay between the time of receipt by a remote unit of transmissions from a lead unit to the time of transmitting a reply by the remote unit transmission to the lead unit. These systems further include a delay time for the lead unit to transmit after the transmission of another unit which is the sum of a one and one half seconds plus an additional time determined from the twelve addressing bits currently used for the addressing of the lead and remote units in a manner analogous to that described above with reference to U.S. Pat. No. 3,380,399. Thus, prior systems, while providing a non-fixed time period between transmissions of different lead units did not contain an overall effective system for accurately controlling when different remote units could reply to transmissions from a lead unit, nor a system having different time intervals for the transmission of various types of messages measured from the end of the last radio transmission. Such systems did not make any provision for assuring the transmission of the highest priority messages first and transmitting messages of lesser priority after the completion of the transmitting of the higher priority messages.
Prior air braking systems for trains having a lead unit which controlled one or more groups of remote units by a radio communication channel monitored the flow of air in a flow adapter located between a main reservoir and a brake valve relay section in the remote units. Two sensors were connected to the flow adapter such that the first sensor sensed the differential pressure across the flow adapter to determine when the pressure drop across the flow adapter was above a maximum level indicative of a significant flow rate requiring idle down of the remote unit wherein idle down is the stepping down of the throttle to idle and cutting out of the air brake feed valve. The flow adapter was coupled to an accumulator. A choke was coupled between the accumulator and the flow adapter. The second sensor, which was a differential pressure switch, was connected across the choke for sensing when the pressure drop across the choke exceeded a threshold. The accumulator functioned to hold the same pressure as the pressure in the flow adapter during steady state conditions. However, a rapid change in the flow rate between the main reservior and the relay valve causes a differential pressure to be created across the choke whch was sensed by the differential pressure switch. Any rapid change in the flow rate (e.g. 5 psi pressure differential) could at times cause the differential pressure switch to trip. Any tripping of the differential pressure switch may be intrepreted as a condition resulting in the unnecessary idle down of the remote unit. The differential pressure switch was mechanical and functioned to produce an indication of any threshold differential pressure greater than its sensitivity during a time interval greater than its response time capability. Effectively, the differential pressure switch functioned almost instantaneously to produce an output signalling a rapid flow rate into the brake pipe. The differential pressure switch was at times susceptible to being tripped by transient conditions such as those that might occur when a train is being pulled out of the yard in the morning under conditions of extreme cold when the various air fittings of the brake pipe are being stressed. These short transient air flows do not warrant the idle down of the remote unit.
Prior air brake systems utilized an unregulated equalizing reservior for sustaining the pressure in the train brake pipe during application of the air brake. Once the air brakes were applied, the equalizing reservoir was shut off from the pressure regulated main reservoir which left the equalizing reservoir in an unregulated air pressure state. Without application of a regulated source of air to the equalizing reservoir, certain conditions can cause the variation of the pressure in the equalizing reservoir from that which was applied during the initiation of braking. Variation of the pressure in the equalizing reservoir can lead to either the increase or decrease of the braking action from that which was desired. If a train were traveling into a tunnel where the temperature was warmer than the ambient temperature of the equalizing reservoir, the warmer temperature of the tunnel can at times cause heat to flow into the equalizing reservoir to cause a rise in pressure sufficient to tend to cause the brakes to decrease. If the train were going downhill while traveling into the warmer tunnel, the increase in pressure in the equalizing reservoir could be translated by the relay valve into a release of the brakes which could result in a decrease in the ability to properly control the train. If a train was traveling into an area where the ambient temperature was colder than the temperature of the equalizing reservoir, such as a tunnel in the summertime, the pressure in the equalizing reservoir could drop with the flow of heat out of the equalizing reservoir. A pressure drop in the equalizing reservoir could at times cause the brakes to be applied harder which could lead a decrease in the ability to properly control the train within the tunnel. Restarting of the train could require extensive preparations.